We have been informed by the Central Bureau for Astronomical Telegrams
(IAU Circulars 7094, 7095, 7100), Dr. Howard Bond, Space Telescope Science
Institute, and Dr. Chryssa Kouveliotou, NASA Marshall Space Flight Center and
BATSE Team member, that a gamma-ray burst accompanied by an unprecedentedly
bright optical flash has been detected by the Burst and Transient Source
Experiment (BATSE) instrument aboard the Compton Gamma Ray Observatory
satellite on January 23.40764 UT, and by the Gamma Ray Burst Monitor
instrument aboard the BeppoSAX satellite on January 23.40780 UT. The BeppoSAX
Wide Field Camera 1 also detected the burst and observed the x-ray counterpart.

Interested astronomers were immediately alerted via BATSE's Gamma Ray Burst
Coordinates Network. C. W. Akerlof and T. A. McKay, University of Michigan,
report on behalf of the Robotic Optical Transient Search Experiment (ROTSE)
collaboration (Michigan/Los Alamos National Laboratory/Lawrence Livermore
National Laboratory) that within 30 seconds, the ROTSE-I telephoto camera
array at Los Alamos, NM, which uses an unfiltered broadband CCD, was observing
the location of the gamma-ray burst, and it observed a very bright,
rapidly-fading object. Six observations made between January 23.407851 and
January 23.414677 (approximately 10 minutes) showed the object brighten from
V magnitude 11.82 to 8.95 and then fade to 14.53. Images of these six
observations may be seen athttp://www.umich.edu/~rotse/gifs/grb990123/990123.gif.

Additional observations of the immediate region around this event, obtained
by numerous astronomers at several institutions (see IAU Circulars 7094, 7095,7096, 7098, 7099, 7100), indicate that the optical counterpart of the
gamma-ray burst continued to fade very quickly, reaching R magnitude
approximately 18 in less than 4 hours and fainter than R magnitude 19 in less
than another 5 hours, and fainter than R magnitude 21 in another 24 hours.

The position of the optical counterpart was reported by S. C. Odewahn, J. S.
Bloom, and S. R. Kulkarni, California Institute of Technology, on behalf of
the Caltech-NRAO-CARA GRB Collaboration (IAU Circular 7094) as:

R.A. = 15h 25m 30.5s Decl. = +44 degrees 46' 00" (2000)

This event is potentially a very important one for our observers because the
bright optical flash may occur again once or several times, and so the area
should be monitored. As Dr. Bond explains, "...An exciting aspect of this
object is the suggestion by S.G. Djorgovski et al. that GRB 990123 was
gravitationally lensed (which might account for the extraordinary apparent
luminosity). This raises the possibility, emphasized by E. Turner, that the
gamma-ray and optical bursts may recur in the next few days to months, due to
lensing time delays along different paths to the Earth. It would thus be very
worthwhile for AAVSO members to monitor this position constantly, even with
small telescopes or binoculars, to search for such repeated optical transients,
which could in principle even reach to brighter than 8th magnitude for a few
seconds. Precise times, magnitude estimates, and other details should be
determined for any flashes that are seen."

All AAVSO observers - visual observers, photoelectric photometrists, and CCD
photometrists - are strongly urged to monitor this location as much as possible
over the coming months, and to report any sudden brightening to AAVSO
Headquarters immediately. If you see any brightening at the position of GRB
990123, please monitor it constantly and report the timing of your observations
very accurately, to the fourth decimal of the J.D. We recommend that you have
a tape recorder at hand when you are observing and record your observations
into the tape recorder, for the sake of speed.

The answering machine at AAVSO Headquarters is on nights and weekends for your
convenience. Please call our charge-free number (888-802-STAR =
888-802-7827) to report your observations. We also encourage observers to
send observations by fax to 617-354-0665 or by e-mail through the Internet toobservations@aavso.org.

Many thanks for your valuable astronomical contributions and your efforts.

Good observing!

Janet A. Mattei
Director

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